Beneath our feet rumble the trains on the Northern Line, and somewhere out on the street an ambulance screams past St Pancras. But in here it is quiet: the air disturbed only by muttered conversations, long exhalations and the gentle kiss, thunk, kiss of pink meeting black.

There are 18 tables at King's Cross Snooker Club - still pools of smooth, green baize, in a room lined with wood panelling, red banquettes and gilt-framed photographs of the game's luminaries: Doug Mountjoy, Steve Davis, Joe O'Boyle.

Today there are just six men here to play; shuffling around the tables in jeans and tracksuit tops, crouching low, squinting, wrapped up in angles, odds, mathematics.

Afternoons are always quiet. People come in the evenings, when work is over and the train ride home has yet to begin. They come in the early hours of the morning, when the pubs have closed and nightshifts have finished. They push through an anonymous door, up a well-worn flight of stairs and into the bar, where the radio plays and the lights of the slot machines flutter, and up on the flat screen Sky Sports is on with the volume turned down. But they don't come like they used to. Snooker clubs are dwindling.

Snooker is a British game, invented in the 19th century by army officers stationed in India, whiling away the hours during the monsoon rains. It was popular throughout the last century, particularly during the 1970s and 80s, when it enjoyed regular television coverage. More recently it has been challenged by that glamorous American interloper, pool.

In March, Rileys snooker halls went into administration, with the closure of 30 clubs, and the chain's remaining halls were bought up by another company. But those clubs that survive are struggling. A planned refurbishment here at the King's Cross club, part of a London-based chain, may even bring pool tables.

"A lot of clubs have closed over the last two years, particularly since the smoking ban," says John, a former professional player who now works at the King's Cross hall. Junior membership, he adds, is down two thirds over the last decade.

"There are no idols," argues Toni Sokolnicki, a club regular. "There's no Tiger Woods in snooker, no Wayne Rooneys. In the 80s there was more money put into promotion, but then the top 16 players started getting paid more and it went a bit skewwhiff. It was very much a televised sport then too. Now it's just the world championships on the BBC."

Toni has been coming here since 1985. "It's a twilight zone," he says. "But it's an escape from everyday life." He will be 55 this year and, currently unemployed, he spends four to five hours a day here. He helps out around the club in exchange for free time on the tables.

"It taxes your brain, your mind, your body, taxes your coordination," is how he explains his love of the sport. "It's a horrible, frustrating game. It's great when you're potting balls, but the next day you might not play as well. A lot of people have tempers, it's the frustration, and eventually you throw your cue. The anger is only at yourself."

Today he is playing with Vagan, who moved here from Russia only able to play billiards. For the last two years he has been coming here most days. "We met here," says Toni. "Snooker's very much like that. There's no social life outside the club. We gather as a group, but we don't know much about each other. You tend to say, 'Who's that? How good is he? Would you like a game?'"

This is the club's busiest time of year, these weeks still flushed with the success of the world snooker championships. It attracts novices, people curious about the game they have seen on TV. "They're all sheep," smiles Toni. "But it's nice to see the place full."

Next month, the club will settle back into its old routine. Quiet afternoons filled with cool, dark air and shuffling bodies. The brush of blue chalk, the sliding of cues, the rumble of trains beneath their feet.